Safety switch

ABSTRACT

A safety switch for connection in a circuit to an electric machine has at least one contact closing member which is held in a position to close the circuit so long as current flows through an electromagnet coil connected to a supply. If the current fails the circuit cannot be reclosed on resumption of the current until a push button on the switch is pressed. A safety device comprising a bimetal strip may be provided to close the switch in the event of current overload.

I United States Patent 11 1 3,675,177 Ellenberger 1 1 July 4, 1972 541 SAFETY SWITCH 3,295,077 12/1966 Shaffer et al ..335/19 1,874,797 8/1932 Pavitt ..335/20 X t k b l b [72] men or 11:12, 651,111?" Ahdorf i 'Nuem 3,117,255 l/l964 Peterson ....335/276 x [73] Assignee: Ellenberger & Poenigen Gmbll, Altdorf FOREIGN PATENTS 0 PP AT ONS Nuemberg Germany 1,289,173 2/1969 Germany ..337/66 [22] Filed! Oct. 26, 1970 Primary Examiner-Volodymyr Y. Mayewsky [21] Appl' 83892 Assistant Examiner-DewittM. Morgan An0rney-Harness, Dickey & Pierce 30] Foreign Application Priority Data Oct. 27, 1969 Germany ..1 19 53 984.5 [571 ABSTRACT A safety switch for connection in a circuit to 'an electric [52] v US. Cl ..337/66, 335/19, 337/72 machine has at hast one Contact closing member which is mm [51] lnt.Cl ..ll0lh 71/40, l-lOlh 71/58, HOlh 83/06 in a position to dose the circuit so kmg as current flows [58] held of Search '5';$ 337/62 through an electromagnet coil connected to a supply. if the I 6 372 current fails the circuit cannot be reclosed on resumption of the current until a push button on the switch is pressed. A [561 Rderences Cited safety device comprising a bimetal strip may be provided to UNITED STATES PATENTS close the switch in the event of current overload.

2,895,028 7/1959 Ellenberger ..337/66 X 9 Claims, 5 Drawing Figures fi 35 e a 1 f:

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Patented July 4, 1972 3 Sheets-Sheet 2 INVENTORi JQXQZ 27/6775: 7 kt?" BYI v SAFETY swrrcn BACKGROUND AND SUMMARY OF THE INVENTION This invention relates to a safety switch. Certain known switches are designed as overload switches, so that if a short circuit current passes through them an electromagnet is excited by the current so that an armature is attracted and a retaining projection is pivoted to release a contact closing member and opens the switch. The switch is reclosed when the current is reduced.

The object of the invention is to provide a switch which is opened when the current supply thereto fails, and is not reclosed until a push button of the switch is pressed. Thus, in the event of a breakdown, machines to which the switch is applied do not inadvertently restart when the current supply is restored.

According to the present invention there is provided a switch including a contact closing member movable towards a contact closing position by movement of a push button, and retainable in the contact closing position by a retaining projection which is movable to assume and maintain a retaining position during excitation of an electromagnet. The projection is preferably on a movable armature associated with the electromagnet such that the projection is moved into the path of travel of the first contact closing member when the electromagnet is energized. The armature may be pivoted and cranked, having one limb adapted to contact the electromagnet and having the projection on the other limb.

' If the current supply in the circuit in which the switch is connected fails, the electromagnet is de-energized and the projection is displaced out of its retaining position so that the contact closing member moves to open the contacts. When current is restored, the projection moves back into the restraining position, but no contacts are closed until the contact closing member is moved into its operating position by movement of the push button.

There may also be provided a further contact closing member movable to and retainable in a contact closing position on movement towards and retention in its contact closing position of the first contact closing member. The two contact closing members may, for instance be associated with contacts in the lead and return lines of a circuit to a machine respectively. Thus, with this provision there is no voltage at a machine in the circuit when the supply fails.

The core of the electromagnet may be U-shaped, having a coil on one limb. If the armature is pivoted and cranked it may be pivoted about a comer of the end of the other limb of the core, and may be held thereagainst by a leaf spring. The ends of the core are suitably coplanar. One arm of the cranked armature may be substantially parallel to the limbs of the U- shaped core, the arm supporting the projection. Accurate and simple mounting of the armature can be obtained, with a small air gap between the armature and electromagnet, but nevertheless a sufficiently great range of movement of the projection.

The first contact closing member may be axially movable with play on a rod attached to the push button, its axial movement being limited in one direction by abutments about which the member is pivotable to engage extensions on the rod, by means of which extensions the member may be moved towards the contact closing position on inward movement of the push button.

In order to assure that the extension on the rod will engage the contact closing member, there may be an abutment on the housing, inclined to the rod, and against which the member, when not restrained by the projection, is urged. The inclination of the abutment is such as to allow the extensions to engage the contact closing member when the push button is nex pushed in.

To protect an associated machine or apparatus against overcurrent through a switch according to the invention, there may be provided a bimetal strip associated with a heating coil which is bendable when a current of greater than a predetermined value passes through the coil such that the strip moves the projection from the restraining position.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an elevational view of one form of switch according to the invention when the switch is open;

FIG. 2 shows the same view as in FIG. I, but with the switch closed;

FIG. 3 shows a similar view to that of FIG. 2 of a second form of switch according to the invention, also when closed, having a heated bimetal strip;

FIG. 4 shows a schematic diagram showing the principle of operation of the switch of FIGS. 1 and 2; and

FIG. 5 shows a schematic diagram showing the principle of operation of the switch according to FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The switch illustrated in FIGS. 1 and 2 has a housing consisting of two housing halves, only one of which, 1, is shown. In the housing is an electromagnet 2 having a one piece U- shaped core 3, preferably made from a soft magnetic material of high initial permeability and a low coercive field strength, a magnet coil 4 about a limb 6 of the core, and an armature 5. The cranked armature 5 is pivotable about a comer 10 of the end of the limb 7 of the core, and is held thereagainst by a leaf spring 16 held between projections-17,18 in the housing. A short circuiting ring 6' is pressed on the end of the limb 6 of the core, and retains the coil 4 on the limb. The ends 8 and 9 of the limbs 6 and 7 are ground to be coplanar. The armature- 5 has a limb substantially parallel to the limb of the core, and a projection 15 is mounted on this limb. One end 1 1 of the coil 4 is electrically connected to a lug 12, the other end 13 of the coil 4 being electrically connected to a terminal lug 14.

A push button 19 is rigidly connected with or made integral with a rod 19' slidable in the housing and of insulating mater-ial. At the lower endof the rod 19 is a switching bridge 20 made from a piece of sheet metal. The switching bridge 20 has an extension 21 and, on each side of the rod 19 an abutment 22 on which is supported, and on which is pivotable, a switching member or contact closing member 23, in the form of a cranked lever. An upper arm 24 of the switching member 23 has at its center a bore surrounding rod 19' with play, so that the member 23 can pivot on abutments 22 and move axially of rod 19. The arm 25 carries a contact 26 adapted to cooperate with a fixed contact 27 on the housing, the contact 27 being connected to a lug 28. A conducting cable 29 connects arm 25 of the switching member 23 to a bent-over portion 30 of a connecting lug 31. The arm 25 has on both sides a bent-over portion having a step 32 which can cooperate with the extensions 21 on the switching bridge 20.

An insulating disc 33 having a bore for guiding the switch rod 19' is inserted in a recess in the housing, while the rod 19' is also guided by the abutments 22 engaging in grooves 34 in the housing. Between the push button 19 and the disc 33, is a compression spring 35, which urges the push button 19 out- I shown in FIG. I. In this position of the switching member the steps 32 on the arm 25 are positioned to be contacted by the extensions 21 on the switching bridge 20 so that, when the push button 19 is pushed in, the switching member 23 is urged towards the contact closing position, but remains inclined to rod 19' so that contacts 26, 27 do not touch each other. When the electromagnet is then excited, the projection 15 on the armature 5 moves counterclockwise as shown, and causes the switching member to pivot until contacts 26, 27 close as shown in FIG. 2. The switching member remains in this position until current to the electromagnet is discontinued.

A contact bridge 40 is displaceably mounted on rod 38, its

movement being limited by a collar 42 on the rod, against which it is urged by a compression spring 41. As shown in FIG. 1, collar 42 is above contacts 44, so that these contacts are not closed by the contacts 43 on the bridge 40. In the FIG. 2 position the rod 38 has been moved downwards with the switching member 23 such that bridge 40 is springurged to join the contacts 43 and 44, the collar 42 now being below the contacts 44, which are connected to lugs 45.

The switch of FIGS. 1 and 2 operates as follows. If the switch is initially disposed as shown in FIG. 1, a mains voltage applied to lugs 12 and 14 excites the electromagnet 2 which attracts the armature 5. The armature pivots so that the projection 15 is displaced into the path of travel of the switching member 23, i.e., into its position of FIG. 2. To close the switch, the push button 19 is depressed, thus compressing spring 35. The switching bridge moves downwards with the push button, as the extensions 21 engage the steps 32 on the switching bridge. The right-hand end of the arm 24 of the switching member 23 engagesthe projection 15 from above, and urges it, against the force of the electromagnet, to the right as shown. The projection returns to its retaining position when the arm 24 has passed downwardly below it.

The push button 19 is then released, and the switching member begins to move upwards, until stopped and rotated by the projection 15. The member rotates quickly so that the contacts 26 and 27 are closed. This switching on movement is rapid so that contacts 26 and 27 are protected from damage. No further upward movement of the switching member 23 occurs.

While the switching member 23 is being moved to its contact closing position, it also pushes the sliding rod 38 downwardly against the action of spring 39. The collar 42 is thus moved below contacts 44, so that the bridge 40 is urged by spring 41 to its contact closing position. The switching member 23 and bridge 40 may suitably be connected each in the outward or return line of a current supply to a machine.

The switch in the closed position as shown in FIG. 2, is sen sitive to a failure in current supply to the machine. If the current fails, the electromagnet 2 is de-energized and the projection 15 is no longer held in its retaining position, but is rotated out of this position by the switching member being urged upwardly out of its contact closing position by the spring 35 and mature 5. The bimetal strip 47 has a heating coil 56 the upper end of which is electrically connected with the bimetal strip and the lower end of which is electrically connected with a connecting lug 57.- The cable conductor 29 connects the switching member 23 with the bimetal strip 47 and thus with the heating coil 56.

If an excess current passes through the switch, the coil 56 heats the bimetal strip so that it bends to such an extent as to pivot the armature 5 clockwise as shown to remove the projection from its switching member retaining position. The

switching member then moves from its contact closing position to open the switch. a

All connecting 'lugs 12, 14, 28, 31, 45 and 57 may be designed as plug-in connections and/or as soldered connections. I

FIGS. 4 and 5 show schematic diagrams of the method of operation of the switches of FIGS. 1 and 2 and of FIG. 3 respectively. In both Figures the connecting lugs 12 and 14 of the coil on the electromagnet are shown, and a current must be present in the coil to allow current to fiow in the lines to a machine, these lines being represented at the top of the Figures. In addition, to complete the circuit of FIG. 4 to a machine, the contacts between points 28'and 31 and 45 45 must be closed. These points correspond to similarly numbered lugs in the switch of FIGS. 1 and 2. In the FIG. 5 diagram, point 57 corresponds to lug 57 in the switch of FIG. 3. As in this case the coil carries current which follows a path between lug 28, switching member 23, limb 55 of the armature and the'bimetal strip to lug 57, the bimetal strip coil 56 only conducts current when the electromagnet is excited, and

by the spring 39, which overcomes the oppositely disposed spring 41. The switch then returns to the position of FIG. 1, with the switching member 23 against the inclined face 36 on the housing. Upward movement of the switching member 23 will occur whether or not the push button 19 moves outwardly, this being an advantageous arrangement in case the push button becomes jammed, both lines to a machine nevertheless being broken. When the current supply is restored, the switch will not be closed until the push button has again been pushed in to move the contact closing member 23 and bridge 40 to their contact closing positions.

A further embodiment of switch according to the invention is shown in FIG. 3. The switch of FIG. 3, which is shown in the contacts closed position, has the additional features over the previously described switch of a bimetal strip 47 to which is welded an angle member 49 an arm 50 of which projects perpendicular to the bimetal strip 47. The bimetal strip 47 is held spring 52 supported on the projection 17 on the housing acts on the angle member 49 and therewith on the bimetal strip 47. Screwed into the arm 50 is a screw 53 which extends through a slot in the projection 17. The said screw 53 serves'both to secure and to adjust the position of the bimetal strip 47 via the angle member 49, 50. If the screw 53 is tightened, the free upper end of the bimetal strip 47 is pivoted clockwise as shown in FIG. 3. At the upper free end, the bimetal strip 47 has a projection 54 which bears against the arm 55 of the arat its lower end in a slot 46 in the housing. A compression contact between armature limb 55 and projection 54 is maintained. This feature is illustrated in FIG. 5 by the dashed line to the box on the right, in which is represented the bimetal strip which can cause opening of the current path between lug 57 and lug 28.

While it will be apparent that the teachings herein are well calculated to teach one skilled in the art the method of making the preferred embodiments of this invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or meaning of the subjoined claims.

What is claimed is:

1. A switch comprising:

a housing;

a push button carried by said housing;

a contact closing member coactive with said push button and movable towards a contact closing position by movement of said push button;

a retaining projection coactive with said contact closing member and being movable to and from a retaining position, said retaining projection adapted in said retaining position to retain said contact closing member in said contact closing position;

resilient means constantly urging said retaining projection away from its retaining position when said contact closing member is in its contact closing position; and

electromagnetic means operative when energized to cooperate with such retaining projection to move the latter to assume said retaining position and maintain said position by counteracting said resilient means, whereby de-energization of said electromagnetic means will permit said resilient means to move said retaining projection away from its retaining position.

2. A switch according to claim 1, further provided with a second contact closing member having mechanical connec-' 3. A switch according to claim 1, further provided with a second contact closing member having a mechanical connection to said first contact closing member whereby movement of said first member toward its contact closing position will cause said second member to move from a first to a second position, said resilient means urging said second member back toward its first position and also urging said first member by means of said mechanical connection away from its contact closing position and away from said coaction with'the push button, whereby both contact closing members will be moved by said resilient means in response -to de-energizationof said electromagnetic means even when said push button is jammed.

4. A switch according to claim 3, said mechanical connection comprising a rod having one end engaging said first contact closing member.

5. A switch according to claim 4, said rod being slidable in a groove in said housing, said resilient means comprising a compression spring at the end of said rod remote from its connection to the first contact closing member.

6. A switch according to claim 1, said electromagnetic means comprising an electromagnet with a one-piece U 8. A switch according to claim 7, further, provided with a bimetal strip, heating means for said strip connected to said first contact closing member and responsive to an overload traversing said member to move said armature against the force of said electromagnet coil so as to retract said retaining projection from its retaining position.

9. A switch comprising;

a housing;

a push button carried by said housing;

a contact closing member coactive with said push button and movable towards a contact closing position by movement of said push button; I

a retaining projection coactive with said contact closing member and being movable to and from a retaining position, said retaining projection adapted in said retaining position to retain said contact closing member in said contact closing position;

electromagnetic means operative when energized to cooperate with such retaining projection to move the latter to assume and maintain said retaining position;

a bimetal strip bendable by heat and a heating coil to said bimetal strip, said strip being operatively associated with said projection effective to move said projection from said retaining position when an electrical current of greater than a predetermined value passes through said coil;

a slot in said housing, said bimetal strip being supported in said slot, an arm attached to said strip, spring means urging said arm to bend said bimetal strip, and a screw, said arm being positionally adjustable by said screw. 

1. A switch comprising: a housing; a push button carried by said housing; a contact closing member coactive with said push button and movable towards a contact closing position by movement Of said push button; a retaining projection coactive with said contact closing member and being movable to and from a retaining position, said retaining projection adapted in said retaining position to retain said contact closing member in said contact closing position; resilient means constantly urging said retaining projection away from its retaining position when said contact closing member is in its contact closing position; and electromagnetic means operative when energized to cooperate with such retaining projection to move the latter to assume said retaining position and maintain said position by counteracting said resilient means, whereby de-energization of said electromagnetic means will permit said resilient means to move said retaining projection away from its retaining position.
 2. A switch according to claim 1, further provided with a second contact closing member having mechanical connection to said first contact closing member but electrically separated therefrom, said first member being in the feed line and said second member in the return line of an interruptable circuit, and means responsive to the contact closing movement of said push button for moving said second member to its contact closing position before said first member, said first contact closing member being rapidly moved to its contact closing position by pivoting about said retaining projection.
 3. A switch according to claim 1, further provided with a second contact closing member having a mechanical connection to said first contact closing member whereby movement of said first member toward its contact closing position will cause said second member to move from a first to a second position, said resilient means urging said second member back toward its first position and also urging said first member by means of said mechanical connection away from its contact closing position and away from said coaction with the push button, whereby both contact closing members will be moved by said resilient means in response to de-energization of said electromagnetic means even when said push button is jammed.
 4. A switch according to claim 3, said mechanical connection comprising a rod having one end engaging said first contact closing member.
 5. A switch according to claim 4, said rod being slidable in a groove in said housing, said resilient means comprising a compression spring at the end of said rod remote from its connection to the first contact closing member.
 6. A switch according to claim 1, said electromagnetic means comprising an electromagnet with a one-piece U-shaped magnet core, a magnet coil on one limb of said core, said retaining projection being carried by an armature in the form of a cranked lever, means pivotally supporting said armature, one arm of the armature being substantially parallel to the limbs of said core and carrying said projection.
 7. A switch according to claim 6, the faces of said two core limbs being coplanar, the pivotal supporting means for said armature comprising the outer corner of the outer limb of said core and spring means urging said armature against said corner.
 8. A switch according to claim 7, further provided with a bimetal strip, heating means for said strip connected to said first contact closing member and responsive to an overload traversing said member to move said armature against the force of said electromagnet coil so as to retract said retaining projection from its retaining position.
 9. A switch comprising; a housing; a push button carried by said housing; a contact closing member coactive with said push button and movable towards a contact closing position by movement of said push button; a retaining projection coactive with said contact closing member and being movable to and from a retaining position, said retaining projection adapted in said retaining position to retain said contact closing member in said contact closing position; electromagnetic means operative wheN energized to cooperate with such retaining projection to move the latter to assume and maintain said retaining position; a bimetal strip bendable by heat and a heating coil to said bimetal strip, said strip being operatively associated with said projection effective to move said projection from said retaining position when an electrical current of greater than a predetermined value passes through said coil; a slot in said housing, said bimetal strip being supported in said slot, an arm attached to said strip, spring means urging said arm to bend said bimetal strip, and a screw, said arm being positionally adjustable by said screw. 